The priority application number P08-280847 is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a color video signal processor and in particular, to a video signal demodulation circuit used in a multi-color-standard video apparatus.
More particularly, the present invention relates to a baseband delaying circuit for delaying a baseband chroma signal during one horizontal scanning period used in a video signal demodulation circuit for a color system of the multi-color standard systems.
Furthermore, the present invention relates to a color video signal processor and a baseband chroma signal delaying circuit provided on a same large-scale integrated (LSI) circuit chip.
2. Discussion of the Background
In many types of video equipment, such as color television (TV) receivers or video tape recorders (VTR), a baseband delaying circuit is provided in a video signal processor for delaying video signals for one horizontal scanning, period (hereinafter referred to as "IH") in order to demodulate color video signals from a received video signal of a particular type of color standard. The baseband delay circuit is used for delaying a chroma signal an appropriate amount in accordance with a particular frequency range of a delaying target signal.
Presently, there are several types of color TV standard systems for transmitting color television signals, such as NTSC (National Television System Committee) color system, PAL color system and SECAM (Sequenticel Couleur A Memorie) color system. Consequently, a multi-color standard color television receiver has been developed as an export specification in order for the receiver to receive any of a selected appropriate color TV standard in a country of export.
Generally, in a PAL color TV system a received chroma signal is demodulated into two orthogonal phases by changing a demodulation axis every horizontal scanning period. Under the PAL standard, a frequency of about 4.433 MHZ is used as a sub-carrier for the chroma signal. In a SECAM color TV system, a received chroma signal is demodulated with a sub-carrier by alternately changing the subcarrier frequency from 4.40625 MHZ to 4.24 MHZ every horizontal scanning period. A multi-color-standard video apparatus as described above needs a baseband delaying circuit for delaying a received chroma signal during one horizontal scanning period and the delay is usually set to 64 .mu.s, in accordance with a frequency range of a particular received color standard in a given country.
An ultrasonic delaying device or an electronic delaying circuit such as a charge coupled device (CCD) has been used conventionally as the baseband delaying apparatus for achieving the 1H delay. As a propagation medium, a fused glass has been used in the ultrasonic delaying device.
However, the conventional delaying devices have been provided as a separate element from an LSI video signal processor. Consequently, a total system including the video signal processor and the baseband delaying circuit requires a large amount of system real estate. Furthermore, manufacturing cost increases with the increase in system real estate. Accordingly, there are disadvantages to producing a multicolor-standard color video processor having a separate baseband delaying circuit.
As mentioned above, the conventional video signal processor including a baseband delaying circuit has many problems and defects. Instead of using a CCD delaying device, a switched capacitor filter as an electronic delaying device has been considered. In this case, however, it is very difficult to optimize the total system real estate to accommodate the video signal processor and the baseband delaying circuit.